This invention relates to tapered pin-keys for engaging a part to a shaft.
Pin-keys have long been known and used to engage a part to a shaft or vice versa. There are two broad types of pin-keys: axial pin-keys and tangential pin-keys. With either type, the part is bored to receive the shaft and the pin-key is fit into aligned keyways in the part in the shaft. With axial-type pin-keys, the keyway in the part is adjacent to and is generally parallel with the bore for the shaft, and the keyway in the shaft is generally parallel with the shaft's axis. Axial-type pin-keys secure the part against rotational or torsional loads, but do not secure the part against axial loads. With tangential-type pin-keys, the keyway in the part intersects the bore and is oriented perpendicular to the axis of the bore. The keyway in the part can either intersect the center of the bore, in which case the keyway in the shaft would be an aligned diametrical hole, or the keyway in the part can tangentially intersect the bore, in which case the keyway in the shaft would be an aligned tangential groove in the surface in the shaft. Tangential-type pin-keys secure the part against rotational or torsional loading and also against axial loading.
One of the problems with the prior art pin-key and keyway systems was that exact alignment was required between the keyway in the part and the keyway in the shaft. If the keyway and the hole or groove in the shaft were made simultaneously by drilling the keyway with the shaft in place, it was difficult to maintain the interchangeability and replaceability of the shafts and parts because of the tendency of a drill to drift into softer material. Since the shaft and part were rarely of the same material, the drill would tend to drift from the desired line and thus each part and shaft would be slightly different. This problem was especially pronounced with tangential type keyways. Properly aligned keyways could be made but only with special equipment and time consuming and expensive shop procedures. If the part and shaft were to be separately manufactured, precise machining was required to insure that the holes and grooves were properly located. This made the shafts and parts very expensive.
While cylindrical pin-keys and keyways have been used, the majority of prior art pin-keys and key-ways were tapered. The tapered pin-keys and keyways were usually frustoconical in shape and were preferable over the cylindrical configuration because they achieve a tighter engagement between the part and shaft. The cylindrical pin-key had to be made smaller than the keyway to allow the pin-key to be inserted and removed from the keyway. Thus, there was some play between the shaft and part. In contrast, the tapered pin-key, by virtue of its narrowing configuration, could be inserted into the tapering keyway until it was firmly engaged therein on all sides, thereby eliminating the play between the shaft and part. However, while achieving a tighter engagement than the cylindrical configuration, the tapered pin-keys and keyways had a disadvantage in that they were more expensive to manufacture because their manufacture was difficult, time consuming, and required special equipment. In addition, precise alignment was needed between the keyway in the part and the keyway in the shaft.
There were some tapered pin-keys that did not require a tapering keyway. For example, there were cylindrical pin-keys with a tapering flat. This pin-key could be inserted into a cylindrical keyway in the part and engage a flat on the shaft. This type of pin-key was unsatisfactory because the flat was a stress concentrator that could cause failure of the shaft. Furthermore, the flat did not securely hold the part and shaft from axial loading. Another prior pin-key was a cylindrical pin-key with two tapering adjacent flats. The pin-key was inserted into a cylindrical keyway in the part and engaged a V-shaped groove in the shaft. This type of pin-key was also unsatisfactory because the V-shaped groove in the shaft was a stress concentrator that could cause failure of the shaft. Furthermore, the pin acted like a wedge under torsional loading which could also cause failure of the shaft.
The inventor's prior invention, which is the subject of co-pending application Ser. No. 496,004 filed May 19, 1983, and incorporated herein solved many of these problems by providing a tapered pin-key having two cylindrical surfaces converging at a small angle. The pin-key fit in a cylindrical keyway tangentially intersecting the bore for the shaft. The tangential keyway was preferable to the keyway extending through the center of the bore, because far less shaft material is removed in making a groove aligned with the tangential keyway than in making a hole aligned with a keyway intersecting the center of the bore. Thus, the shaft is left stronger, with more cross-sectional area to bear torsional or other loads. Furthermore, the surface groove has far less stress concentrating effect than the hole through the shaft, or the other shapes of the prior keyways.
The tapered configuration of the inventor's prior pin-key allowed the pin-key to achieve the firm engagement of the prior art tapered pins, but because the pin-key was formed from cylindrical surfaces, the pin-key, keyway, and groove all have cylindrical surfaces, and are thus easier and less expensive to make. Furthermore, the precise alignment of the keyway and the groove required for prior art pin-keys was no longer necessary, the pin-key being self-adjusting. Variation in the depth of the groove in the shaft is permissible.
The present invention is an improvement upon the inventor's prior tapered pin-key. The improved pin-key of this invention is similar to the prior pin-key except that it includes an axial cavity in the pin-key. The cavity is sized such that the walls of the pin-key can be elastically deformed to conform to the keyways in the part and the shaft. Thus the pin-key of this invention securely engages the part and the shaft, eliminating any play between them. The pin-key accommodates minor inaccuracies in the formation of the keyways in the shaft or in the part. Because the pin-key conforms to the keyways, it can be made with less accurate and less expensive manufacturing processes, for example casting. Inaccuracies in the shape of a pin-key are accommodated by the deformation of the pin-key.
The pin-key of this invention can be preloaded to elastically deform the pin-key to conform to the keyways before the part and shaft are put into service. One method of preloading the pin-key is to hammer it into the keyway, wedging it into engagement with the part and shaft. Alternatively, the keyway in the part can be threaded at the top so that a cap can be threaded into the keyway to retain the pin-key and to compress the pin-key. In a second alternative, a threaded stud can be provided on the bottom of the pin-key. The stud protrudes through the part when the pin-key is in the keyway. A nut is threaded onto the stud to retain the pin-key and draw the pin-key into the keyway, preloading the pin-key.
The axial cavity in the pin-key is preferably threaded so that a threaded tool can be engaged therein to aid in the removal of the pin-key from the keyway.
The pin-key of this invention permits superior engagement with the keyway in the part and the keyway in the shaft. The elastic deformation of the pin-key accommodates any inaccuracies in the formation of the keyway in the part, the keyway in the shaft, or in the pin-key itself. The pin-key can thus be made with less accurate and less expensive methods of manufacture such as casting. The pin-key of this invention can be preloaded either by physically wedging it in the keyway, by compressing it in the keyway with a threaded cap, or drawing it into the keyway by a threaded stud projecting from the bottom of the pin-key. This preloading allows the part and shaft to be securely engaged before they are put into service.